Raccoon and Skunk Population Models for Urban Disease Control Planning in Ontario, Canada

Abstract

Population data on raccoon (Procyon lotor) and striped skunk (Mephitis mephitis), collected between 1987 and 1996 in the city of Scarborough (Ontario, Canada), were used to develop spatially explicit population models for use in disease control planning. The objective of model development was to: (1) provide a standard analytical method to identify areas of high-density raccoon and skunk subpopulations within cities, and (2) to identify those subpopulations predicted to function as sites of high dispersal (either into or out of subpopulations). These areas could be targeted in disease control programs. The models combined landscape map data with a stochastic, age-structured population model, which incorporated habitat-specific demographic data and functions relating to animal dispersal. Using this approach, the assemblage of raccoons and skunks inhabiting Scarborough was modeled as occupying discrete subpopulations linked by dispersal (i.e., a metapopulation). The landscape data used in this study were derived from classified LANDSAT satellite imagery data. Population data were derived from the literature and from trapping data collected within the Scarborough study area. The resulting models depicted metapopulations containing 7432 ± 1529 raccoons (mean ± 1 sd) distributed throughout eight subpopulations, and 533 ± 125 skunks distributed throughout 10 subpopulations. Raccoon density within subpopulations ranged from 37 to 94 animals/km2. Skunk density within subpopulations ranged from 6.4 to 12.6 animals/km2. Five raccoon subpopulations and one skunk subpopulation were predicted to stabilize at high relative population densities (>125% carrying capacity), implying that these subpopulations were functioning as net importers of dispersing animals. As such, these subpopulations were at higher risk of being sites of rabies outbreaks than surrounding subpopulations, owing to their high population densities and greater likelihood of receiving infected individuals. In contrast, one raccoon subpopulation stabilized at low relative population density and therefore appeared to be functioning as a net exporter of dispersing animals. The disease control implications of these findings are discussed.